The cyclone separator acts as a common classifier or separation equipment, and its working principle is centrifugal settling. A strong rotating shear turbulent motion is generated after the two-phase or three-phase mixture under certain pressure has entered into the cyclone separator from the circumference thereof in the tangential direction. Coarse particles or heavy phase and fine particles or light phase are subjected to different centrifugal force, centripetal buoyancy and drag force etc. due to the granularity or density difference therebetween. Under the action of centrifugal settling, most of the coarse particles or heavy phase is discharged through the bottom opening of the cyclone separator, while most of fine particles or light phase is discharged through over-flow pipe, so as to achieve the object of classifying and separation.
The application of the cyclone separator in the treatment of wastewater containing oil falls within liquid-liquid centrifuging separation technique, which has such advantages as small bulk, lightweight and reduced space requirement and so on. This technique originated from Southampton University, UK in 1970's, when M. T. Thew for the first time used the cyclone separator in oil-water separation. In 1980's, cyclone technique is applied to liquid-liquid separation in petroleum industry, and then in the following twenty years the liquid-liquid hydro-cyclone separator has been improved continually.
The liquid-liquid hydro-cyclone separator separates different substances via the centrifugal force generated by the rotation of fluid. The Chinese Patent CN02239957.7 (Publication Date: May 21, 2003) discloses an oil-water cyclone separator which is suitable to be used for the treatment of wastewater in the process of treating the produced fluid in oil field. The oil-water cyclone separator mainly comprises four revolutions, i.e. inlet section, accelerating section, separating section and steady flow section, wherein the oil outflow pipe is located in the center at the end of the inlet section which is further provided with two tangent inlets. High speed rotation of liquid mixture is generated after the liquid mixture flows from the inlets in tangent direction into the inlet section. Due to different densities of light and heavy components in the mixture, the heavy components, under the action of the centrifugal force, will move toward and concentrate at the wall surface of the hydro-cyclone separator, and then gradually move toward the bottom outlet during rotating, and is finally discharged from the cyclone separator. At the same time, the light components will move toward the central axis of the separator and form an oil core, then flow toward inlet section and flow out through the overflow opening. In this way, the separation of the light and heavy components is achieved.
The previous Chinese Patent CN00217613.0 (Publication Date: Mar. 14, 2001) also disclosed an oil-water cyclone separator. The general structure thereof is similar to the above patent except the accelerating section and the separating section, which have a plurality of taper angles and result in a better separation effect.
The oil-water cyclone separators are generally divided into two types, i.e. de-oiling type and de-watering type. In general, the de-oiling type oil-water cyclone separator is used for treatment of wastewater containing oil (e.g. the oil-water mixture in which the oil-content is less than 2%) to remove the oil thereof. In case the above mentioned oil-water cyclone separator is used to treat wastewater with lower oil content, the oil discharged from the outflow would have a higher water content, and especially the separator will have poor effect when used for separating wastewater with higher oil content or having higher viscosity. In addition, due to different or fluctuating pressures of wastewater containing oil at the inlet section, it is difficult to have a steady oil core flowing in the opposite direction, and thus the separated oil cannot flow out of the small overflow opening smoothly, which might also result in the undesired re-mixing of the separated oil and water.
When applied to solid-liquid separation, gas-solid separation and gas-liquid separation, the cyclone centrifugal separator also has similar problem, i.e. the outlet of light phase and the inlet of the cyclone centrifugal separator are easily communicated to each other, which results in a poor separation effect.